Control means for a hydraulic motor

Abstract: A control means for a hydraulic motor connected to an external load comprises a directional valve (10) for selectively feeding hydraulic fluid to the motor from a pressure source and including load pressure sensing means (24, 25) connected to a load compensating valve (15) located upstream of the directional valve (10) for adjusting automatically the feed pressure in relation to the actual load pressure. The load compensating valve (15) includes a valve spindle (28) with opposite end surfaces (29, 30), one of which is exposed to the load pressure whereas the other is exposed to the feed pressure, and a selectively activatable feed pressure reducing means (38, 43; 50-57) for increasing the bias force acting on the load compensating valve spindle (28) in the closing direction of the latter in relation to the bias force acting in the closing direction of said valve spindle (28).

Description: This invention relates to a control means for a hydraulic motor connected to an external load and which comprises a directional valve for selectively feeding hydraulic fluid to the motor from a pressure source. The directional valve is provided with a load sensing means which is connected to a load compensating valve located upstream of the directional valve and arranged to adjust automatically the feed pressure in relation to the load pressure, which load pressure compensating valve includes a valve spindle having oppositely facing end surfaces, one of which is exposed to the load pressure for biassing the valve spindle in the opening direction, whereas the other end surface is exposed to the feed pressure for biassing the valve spindle in the closing direction. The object of the invention is to accomplish an improved control means of the above type by which it is possible to obtain a certain degree of feed pressure reduction and, accordingly, a motor speed reduction in case very heavy loads are to be handled by the motor, loads that are heavier than what is allowed as maximum load for a particular motor application. This is to avoid hazardous inertia forces when moving a heavy object by means of the motor. A directional valve arrangement of the above type is previously described in EP 0 377 544. This known device, however, comprises two identical units connected to a common pump and having their load sensing passages connected to the load sensing valve via an "or"-element. This results in that the highest load pressure only is supplied to one of the compensating valve end surfaces for accomplishing a feed pressure reduction. Accordingly, the heaviest load dominates and determines the pressure reduction as well as a speed reduction of both loads. The purpose is to ensure that also the heaviest load will be moved in case of an insufficient pump capacity. This device solves a problem opposite to the problem described above, namely to ensure movement of heavy loads. Another prior art hydraulic valve arrangement of the above described type is shown in DE 42 30 183. This known device includes two safety valves V1 and V2 which are intended to connect the load pressure passage to tank, thereby stopping the load movement in case of over-load. The valve V1 is an automatically acting pressure controlled valve, whereas the valve V2 is remotely controlled by an electromagnetic actuator. This arrangement, however, does not offer any means for reducing the load movement speed by increasing the pressure drop across the load compensating valve, and accordingly, it does not solve the above identified problem. The initially mentioned problems are solved by the invention as it is defined in the claims. A preferred embodiment of the invention is described below with reference to the accompanying drawings. On the drawings: Fig 1 shows a longitudinal section through a valve unit provided with a feed pressure reducing means according to the invention. Fig 2 shows, on a larger scale, the load compensating valve in Fig 1, and illustrates the feed pressure reducing means in its inactive position. The control valve unit shown in Fig 1 comprises a housing 14 with a directional valve 10 having service ports 11, 12 connected to a hydraulic motor (not shown). The directional valve 10 also includes an inlet port 13 connected to a pressure fluid source via a load compensating valve 15 and a supply passage 22, two discharge ports 16, 17 connected to a tank, and a valve spindle 18. The latter is shiftable by an external manoeuver means as a lever 19 to direct hydraulic fluid to and from the motor and tank by controlling the ports 11, 12, 13, 16, and 17. The service ports 11, 12 are connectable to the discharge ports 16, 17 by means of pressure controlled shunt valves 20, 21. In the housing 14, upstream of the directional valve 10, there is located the load compensating valve 15 which is arranged to adjust the feed pressure in the inlet port 13 in relation to the actual load on the motor. To this end, the spindle 18 of the directional valve 10 is provided with load pressure sensing passages 24, 25 which are connected to a longitudinal passage 32 in the valve spindle 18 and arranged to be alternatively brought into communication with the service ports 11, 12 as the valve spindle 18 is shifted in either direction to direct pressure fluid out through one of the service ports 11, 12. A passage 27 in the valve housing 14 leads the load pressure from the spindle 18 to the left end of the load compensating valve 15. The latter comprises a valve spindle 28 which has two oppositely facing end surfaces 29, 30 and a central shoulder 31 for controlling the fluid flow past a land 26 in the housing 14 and, accordingly, the feed pressure in the inlet port 13. The right end surface 30 of the compensating valve spindle 28 is pressurized by the feed pressure in the inlet port 13 in that the right end surface 30 communicates with the latter via a central passage 33 and radial openings 34 in the valve spindle 28. At its left end, the compensating valve spindle 28 is acted upon by two springs 35, 36 which together with the load pressure communicated through the passage 27 balance the valve spindle 28 against the feed pressure communicated to the right end surfaces 30 through the passage 33 and openings 34. Depending on the actual load pressure, the fluid passage between the shoulder 31 of the valve spindle 28 and the land 26 in the housing 14 restricts the supply flow to a desired degree determined by the characteristics of the springs 35, 36. At the right hand end of the valve spindle 28, there is movably guided a cup-shaped piston 38 which on its left hand end is acted upon by the fluid pressure in the inlet port 13 supplied via the passage 33 and openings 34 in the valve spindle 28,and which is shiftable by pressure fluid selectively supplied to its opposite end through an opening 39. The piston 38 is shiftable between an inactive position as shown in Fig 2 and an active position as shown in Fig 1. The piston 38 carries a coaxially extending support rod 40 which at its outer end is formed with a head 41. On the support rod 40 there is movably guided a spring supporting washer 42, and a spring 43 which acts between the piston 38 and the washer 42. The washer 42 is arranged to cooperate with a shoulder 37 on the valve spindle 28. An auxiliary spring 44 is inserted between the piston 38 and an end cap 45 on the housing 14 to exert a bias force on the piston 38. In operation, pressure fluid is supplied through the passage 22, passing the shoulder 31 of the compensating valve spindle 28, reaching the directional valve 10 via the inlet port 13 and is directed to the motor through one of the service ports 11, 12. The actual load pressure is communicated from the load pressure sensing passages 24, 25, via the passage 27 to the left end surface 29 of the valve spindle 28 so as to exert a bias force on the latter. Depending on the actual load pressure acting on the valve spindle 28, the fluid flow past the shoulder 31 is restricted such that the feed pressure which prevails downstream the shoulder 31 and which is communicated to the right end surface 30 of the valve spindle 28 will balance the joint bias force of the load pressure and the springs 35, 36 acting on the valve spindle 28 in the opposite direction. When it is desired to activate the motor under very heavy load circumstances the motor speed must be kept down to avoid hazardous inertia forces. This is accomplished by directing pressure fluid onto the piston 38 via the opening 39, thereby making the piston 38 move to the left such that the washer 42 lands on the shoulder 37 on the valve spindle 28. In this position of the piston 38, the washer 42 is lifted off the head 41 of the support rod 40, which means that the spring 43 now is free to act between the piston 38 and the valve spindle 28. Accordingly, an auxiliary bias force is applied on the latter in the closing direction of the shoulder 31 relative to the land 26, which means that the feed pressure in the inlet port 13 is further decreased, as is the motor speed. At deactivation of the feed pressure or speed reducing means, the fluid pressure supplied through the opening 39 is discharged and the piston 38 is moved to the right by the feed pressure prevailing in the chamber between the valve spindle 28 and the piston 38. During that movement of the piston 38, the head 41 of the support rod 40 engages the washer 42 and lifts the latter off the shoulder 37 on the valve spindle 28, thereby removing the auxiliary bias force exerted by the spring 44 from the valve spindle 28. Then, the load compensating valve 15 will resume its normal operation order.

Claims: Control means for a hydraulic motor connected to an external load, comprising a directional valve (10) having load pressure sensing means (24, 25) and arranged to selectively feed hydraulic fluid to said motor from a pressure source, and a load compensating valve (15) located upstream of said directional valve (10) and connected to said load pressure sensing means (24, 25) and arranged to adjust the feed pressure in relation to the actual load pressure and including a valve spindle (28) having oppositely facing end surfaces (29, 30) one (29) of which is exposed to the actual load pressure for biassing said valve spindle (28) in the opening direction of the latter, whereas the other (30) of said end surfaces is exposed to the feed pressure for biassing said valve spindle (28) in the closing direction of the latter, characterized in that said load compensating valve (15) comprises a selectively activatable feed pressure reducing means (38, 43) for increasing the bias force acting on said valve spindle (28) in the closing direction of the latter in relation to the bias force acting in the opening direction of the said valve spindle (28). Control means according to claim 1, wherein said feed pressure reducing means (38, 43) comprises a spring means (43) applicable on said valve spindle (28) in the closing direction of the latter, and an actuating means (40,41) shiftable between an inactive position in which it inhibits the action of said spring means (43), and an active position in which it applies said spring means (43) onto said valve spindle (28). Control means according to claim 2, wherein said actuating means (38) comprises a piston (38) which on its one end is exposed to said feed pressure for being biassed toward said inactive position, and which on its opposite end is selectively pressurized for being actuated toward said active position.

Inventors: MARTYN KYLE GORDON, WENNERBO OERJAN EGON VALDEMAR, MARTYN, KYLE GORDON, WENNERBO, OERJAN EGON VALDEMAR, Wennerbo, Örjan Egon Valdemar
Applicants: VOAC HYDRAULICS BORAS AB
Application year: 1994
Main classification: F15B11
IPC codes: F15B13